PTSD and traumatic exposure add considerably to the national burden of disease. With a retrospectively estimated incidence rate of 88 and 31 PTSD cases per 100,000 PYs for women and men, respectively, this is higher than that of, for example, colorectal cancer (25 and 28) or lung cancer (28 and 32) [
17]. PTSD differs from the major somatic non-communicable diseases (NCDs) (cardiovascular disease, most cancers, diabetes, and chronic respiratory disease) in that it largely appears during the young adult age range. In cases where PTSD is not treated, or does not respond to treatment, but enters a chronic state, people may live more of their lives with PTSD than the other NCDs mentioned.
Main findings
Our study disclosed lower rates of trauma exposure compared to what has been reported in previous gender-specific epidemiologic studies, as summarized by Olff et al. [
18]. When comparing incidence rates of traumatic exposure across studies and populations, one needs to consider the questionnaires applied and the events included in each. In addition, there are likely differences between populations regarding what constitutes a traumatic event [
19]. It has been hypothesized [
20] that the majority of events involved in survey instruments are traumas more likely to happen to men than to women. In our study, the proportion of men having experienced the trauma was greater in four out of nine trauma types. In addition, the M-CIDI includes an “other traumatic events” category, allowing respondents to include all experienced traumas.
Our results suggest an increased risk of subsequent PTSD for women having suffered from one or more psychiatric disorders prior to traumatic exposure. Had a measure of problematic drinking been included in “Any pre-existing psychiatric disorder,” the gender difference would probably have attenuated. Studies have shown that men to a greater extent than women attempt self-medication using alcohol against mental health problems [
21]. A psychosocial explanation for the increased risk for PTSD in individuals with pre-existing psychiatric disorder would suggest that the conditions under which people with psychiatric illness may live either socioeconomically or in strained personal relationships, predispose them to increased chances for experiencing a traumatic event. Another explanation would indicate that being emotionally wounded puts you at risk of a traumatic event. Women are often considered more sensitive to interpersonal stress, with a higher sense of guilt [
22]. In this scenario, the illness is related to personality factors that augment susceptibility to trauma. This warrants further study.
The fact that women more often than men fulfill diagnostic criteria for PTSD may be construed to mean that women are more vulnerable and less resilient. However, this may simply be a reflection of the fact that women and men are exposed to different types of potentially traumatic events. This study revealed that women more often were exposed to rape, sexual abuse as a child and verbal threats or violence from close relations. These are events associated with stigma and silence. Research on gender and coping has concluded that while men typically externalize, women typically internalize their reactions to stress [
23]. Men tend to focus on changing the stressor, and women focus on changing how they react to the stressor. However, the gendered behavior pattern may be less important than the differences in the nature of traumas experienced. We hypothesize that unaddressed and untreated trauma more frequently will result in PTSD.
There is agreement in the literature that traumas of interpersonal violence are most likely to result in PTSD [
24]. Our results support this. In accordance with previous research, e.g., [
25], we found that men more often than women were exposed to PTEs. Accidental traumatic events, i.e., events not intentionally aimed at the individual (war, natural catastrophe, serious accident, witness trauma happen to others, or verbal threat/violence from non-close relation), resulted in PTSD nearly twice as frequent for men (
p < 0.001). This may indicate that men are less risk-averse. Concurrently, there was no statistically significant difference to the frequency at which premediated traumas, i.e., events aimed at the individual suffering the trauma (physical threat with weapon, rape, sexual abuse, imprisonment/taken hostage/kidnapped, or verbal threat/violence from close relation), resulted in PTSD for women and men.
This study supported PTSD as a young adults’ disorder. While the incidence of trauma per 100,000 PYs sharply increased from age 40, the incidence of PTSD tapered off at the same age, most pronounced for men. Our findings contradict Dorrington et al. [
25] who found reports of traumatic events to reduce in older age. Despite having a limited number of cases, our results do suggest that, particularly for men, resilience might be acquired through life experience and maturing.
Some differences were found in what traumatic events were endured at the rural and urban site, as well as different age of occurrence. These differences are difficult to explain. Living conditions do differ both in the social and professional contexts. The mentioned variations were too small to make assumptions about any significance, but do warrant further investigation.
The information uncovered here underlines the complexity of the PTSD diagnosis. The histories leading a trauma victim to become a PTSD patient come in multiple forms. Particularly among women, our results disclosed longer incubation time from trauma to PTSD. For both genders, the longevity of the PTSD exceeded the expected. According to ICD-10 diagnostic guidelines, PTSD is a diagnosis of transient character, typically not surpassing two years. It may well be the case that one, or more, less severe traumatic exposures, or life-events, later than the worst one, was the triggering event for the onset of PTSD. The unpleasant feelings resulting from the worst traumatization may be kept in control, as a subclinical state, until such a trigger event happened. This is in accordance with the human ability to relate new experiences with old ones, as described in Janet’s theory of dissociation [
26]. Site-specific bodily memories of traumatic experiences may be reawakened decades later by rather innocent events, leading to diagnosable PTSD [
27]. This is also a known phenomenon in the veteran’s literature [
28]. Clinical experience shows that women who have been exposed to domestic violence, sexual abuse or rape may be exposed over a long period of time and are reluctant to and need a long time to disclose their situation and seek help. Such longstanding exposure and hesitation to help-seeking may give rise to a delayed development of PTSD [
27]. We are aware of the controversy surrounding the PTSD diagnosis [
25], both regarding potential diagnostic inflation [
29] and the A criterion [
30].
Strengths and limitations
This study provides an estimate of the incidence and prevalence of PTSD in a western, general population. Most studies of post-disaster PTSD lack information about study participants’ pre-disaster mental health status. Hence, when such studies refer to ‘incidence,’ this should often rather be referred to as ‘prevalence’ at a post-disaster point of time. The use of the CIDI instrument in this study provided the opportunity of calculating incidence rates of both PTEs and PTSD per person year.
Stratifying on gender was a main objective of the present study. While much of the literature identifies differences between women and men on trauma exposure and PTSD incidence, most report results and forms their conclusions across genders, e.g., [
5,
6,
25].
This study may include a small number of cases (exposed to trauma and PTSD). However, detailed information about each person may be a significant contribution to points of departure for further studies on coping, vulnerability, and prevention. Furthermore, it adds to the body of knowledge concerning future classification of PTSD in diagnostic systems. We are aware that work is underway toward including a diagnosis of complex post-traumatic stress disorder or DESNOS in ICD-11 [
31].
Concerning the validity of the diagnoses, we can only refer to the excellent test–retest reliability of the CIDI internationally [
14], and refer to the difficulties with doing validity studies because of the lack of a gold standard for the diagnoses.
This study population had a lower response rate among the young, especially men. As PTSD is a young person’s disorder, there was a need to adjust for this. This was done using inverse probability weighting, adjusting the sample to reflect the composition of the Norwegian population. This study population, as well as most epidemiological questionnaire/interview studies, has a slight selection bias toward being healthier than the general population [
32]. Our results, therefore, likely underestimate the true incidence and prevalence. Any study design will favor the participation of those whose general health allows them the physical ability to participate, and who coped well enough with their trauma to participate. Some of those most severely affected may be deceased, or in a state of health not allowing them to complete the interview. As always, there is a risk of recall bias when asking respondents about the past. This will also act to bias our findings, as some respondents might fail to recall previous exposure to trauma and/or subsequent reactions comprising PTSD and the resulting estimates of incidence and prevalence will be biased in a negative direction. Contrary, recall bias may also overestimate findings, because trauma/non-trauma was decided retrospectively, and this judgement could likely be affected by the current psychopathological state.
The Norwegian context should be taken into consideration. Norway has not seen war on home-soil since 1940–1945, and has only sparingly been involved in UN peacekeeping operations and other war-like situations. During the lifetime of our study participants, up to end of follow-up, Norway saw no major terrorism, with exception of WWII (1940–1945). In addition, Norway has low rates of criminal violence. Natural catastrophes have largely been limited to avalanches and rock slides. There have been a number of shipwrecks and other industry related accidents throughout the period.
Public health and clinical implications
Exposure to potentially traumatic events, and subsequent PTSD, is a public health challenge. Some traumatic events, e.g., natural catastrophes, occur randomly, and are non-preventable. However, other events, e.g., rape, are very much preventable. As shown in this study, the most harmful traumatic events are indeed the preventable ones. Having this knowledge, society should intensify efforts to prevent traumas and provide adequate follow-up to individuals exposed to trauma. Public health education needs to be further targeted at reducing stigma and silence regarding personal traumatic exposure. The potential for prevention and help in processing traumatic events to avoid PTSD may be vast for both women and men.
In encounters with a traumatized individual, crisis intervention should always include an assessment of the individual’s past history of mental health, not least because of the increased risk of developing PTSD after pre-existing mental health problems.